Priority is claimed on Japanese Patent Application No. 2003-147588, filed May 26, 2003, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an eccentric optical system and an optical apparatus using the eccentric optical system. In particular, the invention relates to an eccentric optical system and an optical apparatus using the eccentric optical system, that can be employed appropriately when focusing on a focal plane.
2. Description of Related Art
It is well known that, depending upon the field of application, catoptric systems conventionally have superior characteristics in comparison to dioptric systems.
The advantages of catoptric systems, are that, since chromatic aberration does not occur, provided reflective materials and reflective coatings are permitted by reflection spectroscopy characteristics, an extremely wide range can be covered, the optical path can be folded and the overall optical apparatus can readily be of compact configuration, and provided the curvature is the same, power is increased by a factor of four so that the curvature can be small, thus controlling the occurrence of aberration, and the like.
Catoptric systems are employed in such fields as astronomy and the like, wherein catoptric systems such as Cassegrain and Gregorian types and the like employing a combination of primary and secondary mirrors are well-known. However since these mirrors are positioned on the same axis, the secondary mirror part is shielded, resulting in a light loss.
To improve this point, a variety of catoptric systems being eccentric optical systems of a type employing a combination of a plurality of reflection surfaces mutually eccentric and inclined have been designed. As an example of such a catoptric system, a system having a plurality of reflective mirrors is disclosed in patent documents 1 through 4.
On the other hand, a variety of catoptric systems being a prism type of eccentric optical system wherein a plurality of reflection surfaces are mutually eccentric and inclined have been designed (for example, patent documents 5 and 6).
These eccentric systems are employed as optical apparatus in combination with photodetectors and the like.
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. Hei 7-146442 (FIG. 2)
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. 2000-199852 (FIGS. 1 and 4)
[Patent Document 3]
U.S. Pat. No. 4,265,510 (FIGS. 1 and 3)
[Patent Document 4]
U.S. Pat. No. 4,834,517 (FIGS. 2, 4, and 6)
[Patent Document 5]
Japanese Unexamined Patent Application, First Publication No. Hei 8-122670 (pages 3 to 5, FIGS. 3, 4, and 6)
[Patent Document 6]
Japanese Unexamined Patent Application, First Publication No. 2000-321500 (pages 12 to 14, FIGS. 1 to 12)
With the technology disclosed in patent documents 1 through 4, a plurality of reflective mirrors having surface reflection surfaces is employed in combination. Therefore, in order for each reflection surface to be positioned accurately, it is necessary to machine the relative position of the peripheral part of each reflective mirror and the reflection surface, with high accuracy. Furthermore, it is necessary to position each reflective mirror accurately in relation to the others. During assembly, therefore, an extremely accurate positioning technique, or a positioning mechanism, is necessary to adjust the position of each reflective mirror. As a result, except for the manufacture of optical components, costs are incurred in assembly and adjustment.
Moreover, with the technology disclosed in patent documents 5 and 6, the prism is provided with an incident surface, an emission surface of a transmission surface, and two or three reflection surfaces, and is configured so that the input light is reflected within the prism, and an image is formed after its emission from the prism. At this time, the optical paths within the prism intersect in a triangular shape due to reflection from to the reflection surfaces.
In such cases, the optical paths within the prism intersect in a triangular shape at the point of intersection of the optical axes and the two points of reflection, folding the optical path, and thus permitting a certain degree of miniaturization. In practice, for example, when configuring an optical apparatus having a large incident aperture and a long focal distance, the length of the optical path itself is increased, and back-focus becomes longer.